Various methods of manufacturing a pneumatic tire, in which a green tire is molded on the outer peripheral surface of a metal rigid inner mold, and the molded green tire is placed inside a curing mold along with the rigid inner mold for curing, have been proposed as described, for example, in Japanese patent application Kokai publication No. 2001-88143 and Japanese patent application Kokai publication No. 2003-340824. The manufacturing method using such a rigid inner mold does not require a conventionally used bladder made of rubber, and can eliminate the process of, for example, detaching the molded green tire from a making drum. Moreover, compared with the case where a bladder is used for manufacturing, there is an advantage in that the inner peripheral surface of the cured tire can be formed into a predetermined shape with high precision.
However, because the green tire is pressed by the curing mold from only the outside during the curing, the pressing force acting on the inner peripheral surface of the green tire is small. Accordingly, for example, even when non-uniformity in the volume of the tire constituting members exists on the inner peripheral surface of the tire, it is difficult to correct the non-uniformity, and thus improvement in uniformity of the cured tire is limited.
In addition, when the inner peripheral surface of the green tire is pressed by the outer peripheral surface of the rigid inner mold, spaces between divided bodies forming the rigid inner mold leave marks on the inner peripheral surface of the cured tire, and thus there is a problem of reduced appearance quality.
Moreover, although butyl rubber is mainly used for an inner layer (innermost peripheral surface) of the green tire, an additional work of, for example, applying release agent is needed in order to easily release the inner layer from the outer peripheral surface of the rigid inner mold.
Furthermore, using an inner layer formed of butyl rubber is disadvantageous in reducing the tire weight because an inner layer formed of butyl rubber needs a certain thickness to secure sufficient air penetration preventing performance. For this reason, an inner layer which is light in weight and excels in air penetration preventing performance has been demanded.
An object of the present invention is to provide a method of manufacturing a pneumatic tire, which enables a pneumatic tire having excellent uniformity to be manufactured efficiently, the pneumatic tire having an inner layer which is light in weight and excels in air penetration preventing performance.
A method of manufacturing a pneumatic tire according to the present invention to achieve the above-described object is characterized in that a primary molded body is formed by fitting bead rings on opposite ends, in a width direction, of a cylindrically-shaped body in which at least a carcass material is mounted on an outer peripheral side of a film formed of a thermoplastic resin or a thermoplastic elastomer composition obtained by blending a thermoplastic resin with an elastomer; the primary molded body is set to be sucked and held to an inner peripheral surface of a transfer and holding mold; a cylindrically-shaped rigid inner mold including multiple divided bodies is inserted inside the primary molded body; thereafter suction by the transfer and holding mold is stopped, and the primary molded body is transferred to an outer peripheral surface of the rigid inner mold; next, opposite ends of the carcass material in a width direction thereof are turned up on the rigid inner mold, while other tire constituting members are stacked on an outer peripheral surface of the primary molded body so that a green tire is molded; the green tire is disposed, together with the rigid inner mold, inside a curing mold installed in a curing apparatus; and the rigid inner mold and the curing mold are heated to a predetermined temperature and the film is pressurized from an inner peripheral side to be inflated, so that the green tire is cured and the film is brought into close contact with and bonded to an inner peripheral surface of the tire; next the cured tire is taken out of the curing apparatus; and the rigid inner mold is detached from the cured tire.
Here, when the primary molded body is sucked and held to the inner peripheral surface of the transfer and holding mold, it is also possible that the transfer and holding mold is disposed at an outer peripheral side of the primary molded body, and the primary molded body is pressurized from an inner peripheral side of the primary molded body, while the primary molded body is sucked by the transfer and holding mold from an outer peripheral side of the primary molded body. When the green tire is cured, the film is pressurized to be inflated from an inner peripheral side with a pressure of 0.01 MPa to 3.0 MPa. Moreover, for example, air is sucked from an inside of the curing mold to an outside, while the green tire disposed inside the curing mold is cured.
According to a method of manufacturing a pneumatic tire of the present invention, a primary molded body is formed by fitting bead rings on opposite ends, in the width direction, of a cylindrically-shaped body in which at least a carcass material is mounted on the outer peripheral side of a film formed of a thermoplastic resin or a thermoplastic elastomer composition; the primary molded body is set to be sucked and held to the inner peripheral surface of a transfer and holding mold; a cylindrically-shaped rigid inner mold including multiple divided bodies is inserted inside the primary molded body; thereafter, suction by the transfer and holding mold is stopped; whereby the primary molded body can be smoothly transferred to the outer peripheral surface of the rigid inner mold without damaging the film on the inner peripheral surface.
Next, the opposite ends of the above-mentioned carcass material in the width direction thereof are turned up on the rigid inner mold, while other tire constituting members are stacked on the outer peripheral surface of the primary molded body so that the green tire is molded; the green tire is disposed, together with the rigid inner mold, inside the curing mold installed in the curing apparatus; the rigid inner mold and the curing mold are heated to a predetermined temperature and the film is pressurized from an inner peripheral side to be inflated, so that the green tire is cured. Accordingly, unvulcanized rubber of the tire constituting members is pressed against the inner peripheral surface of the curing mold and flows in the circumferential direction, whereby even when non-uniformity in the volume of the tire constituting members exists, the non-uniformity can be corrected. Hence, uniformity of the tires to be manufactured can be improved.
The film is made to serve as a conventional bladder as described above, and moreover, at the time of curing the green tire, the film is brought into close contact with and bonded to the inner peripheral surface of the tire to form an inner layer. This film is formed with a thermoplastic resin or a thermoplastic elastomer composition. For this reason, compared with the conventional inner layer which is formed of butyl rubber, the film is light in weight and has good gas barrier property, and thus manufactured tires are light in weight and have excellent air penetration preventing performance.
In addition, the green tire is disposed inside the curing mold together with the rigid inner mold, whereby a conventional work of detaching the green tire from the making drum is not required, and thus the green tire can be easily disposed at a predetermined position inside the curing mold. Further, the film which serves as the inner layer also functions as a release material between the inner peripheral surface of the tire and the outer peripheral surface of the rigid inner mold, whereby an additional work of, for example, applying release agent is not required. In this manner, the number of work processes can be reduced, and thus the productivity can be improved.